1. Field of the Invention
The present invention relates to a flip chip package manufacturing method. More particularly, the present invention relates to a flip chip package manufacturing method with the combination of a liquid under-filling resin curing process and a thermo-compression flip chip bonding process.
2. The Related Arts
With the advanced technology, all kinds of electronic components inside the electrical devices advance the function such as the operation speed, the integration, the complexity and etc. Meanwhile, as the electronic mobile devices become thinner, lighter and smaller, the sizes of the electronic components and chips also become getting smaller.
Prior flip chip technology using conductive bumps instead of wiring for electrical signal connection is widely known in the chip packaging field, as referred to C4 process. Please referring to FIG. 1A, FIG. 1A is a schematic of C4 flip chip packaging. Pre-solder 102 is covered on each predetermined bond pad 101 of the carrier 10, and the semiconductor chip 1 is flipped to bond onto the carrier 10 for package, such that each conductive bump 11 of the semiconductor chip 1 is electrically connected to the carrier 10 via bonding the conductive bump 11. The overall thickness and the signal transmission path of the package can be reduced due to the electrical connection without wire, thus the method can meet the package trends of light, thin, short and small and is widely used in the chip packaging field.
FIG. 1B is a flow chart of the prior C4 process for chip packaging. The prior C4 process including steps of: providing a wafer in step S101; attaching a grinding adhesive layer onto the upper surface of the wafer in step S102; thinning and grinding the under surface of the wafer in step S103; removing the grinding adhesive layer in step S104; providing a carrier in step S105; cutting the wafer to multiple chips in step S106; flipping chip and bonding to carrier in step S107; reflowing in step S108; filling liquid resin in step S109; curing the liquid resin in step S110; and inspecting the finished product in step S111.
The liquid resin filling process in step S109 of FIG. 1B is to use the resin to fill and seal the gap H between the chip 1 and the carrier 10. The thermal expansion coefficient of the semiconductor chip 1 is about 3˜5 ppm/° C., and the thermal expansion coefficient of the carrier 10 is about 20˜30 ppm/° C. Due to the mismatch of the thermal expansion coefficients is very large, the temperature variation during the package process may cause the stress generated from coefficient thermal expansion difference and damage bonded solder joint. Filling the resin can effectively reduce the stress and therefore enhance the reliability of the package structure and stabilize the product quality. The prior liquid resin filling method mainly uses a dispensing robot dispenser (DRD) to dispense the liquid resin material onto the edge of the chip 1, and the resin material will flow to the bottom of the chip 1 by capillarity to fill the gap H between the chip 1 and the carrier 10.
However, the pitch of the conductive bump and the bond pad becomes smaller which reduces the bonded gap between the flipped chip and the carrier; such that it needs to take more time to fill the space below the chip due to the small flow capillarity phenomena of the resin material. The increasing difficulty of filling the space below the chip leads the existence of the bubbles inside the resin material.
Besides, during the manufacturing process of the multi-chip module (MCM) and multi-chip stack package, the flip chip process is executed for many times. After the reflow high-temperature heating process for many times, the conductive bump of the chip will often be oxidized. It will reduce the adhesion between the filled resin material and conductive bumps. Besides, due to the bonded solder stress generated from the thermal expansion coefficient difference during the heating process for many times, it will degrade the reliability of the mechanical and electrical characteristics of the soldering joint.
Thus, the non-conductive film (NCF) is provided to replace the liquid resin materials, and the thermo-compression flip chip bonding process will executed with the high bonding accuracy, high-temperature and compression method to solve the above problems, wherein the non-conductive film (NCF) is multi-stage hot-cured type and has low modulus in high temperature.
Please referring to FIG. 2A, FIG. 2A is a flow chart of the prior flip chip method with the non-conductive film. As shown in, firstly, a wafer is provided in step S201, and the wafer has multiple conductive bumps on the upper surface of the wafer, wherein the material of the conductive bumps may comprise at least one of tin, silver, copper, gold, indium, lead, bismuth and zinc. The non-conductive film is laminated onto the upper surface of the wafer in step S202, a thinning grinding process is executed to thin and grind the under surface of the wafer in step S203, and then the wafer is cut to multiple single chips in step S204. Then, a carrier is provided in step S205, and a thermo-compression flip chip bonding process is executed to bond the single chip attached with the non-conductive film to the carrier in step S206, wherein the temperature is raised up and the non-conductive film on the single chip is pressed onto the carrier such that the conductive bumps of the single chips pierce through the non-conductive film to make the conductive bump contact with the bond pad of the carrier. Then, a high-temperature compression soldering process is executed with raising temperature rapidly in step S207 to melt the conductive bump to directly solder on the carrier. Finally, a curing process is executed to cure the liquid resin in step S208 and an inspection process is executed to inspect the finished product in step S209.
Please referring to FIG. 2B, FIG. 2B is a press-temperature time curve diagram of bonding process in prior art. As shown in, initially, as the temperature gradually increases to 140° C., the conductive bump of the chip is pressed to 20N to pierce through the non-conductive film, wherein the elastic coefficient of the non-conductive film decreases due to the increased temperature. Thus, the conductive bump contacts the predetermined bond pad of the carrier such to attach the non-conductive film onto the carrier. Then, after confirming the corresponding position of the conductive bump of the chip and the predetermined bond pad of the carrier, the press exerting on the chip is decreased to 1N, and simultaneously the temperature is raised rapidly to melt the conductive bump to even form the eutectic solder to directly solder the conductive bump onto the carrier. As shown in, when the temperature increases to 260° C., the whole flip chip soldering process is finished within several seconds. Executing the flip chip process via the non-conductive film does not require the liquid resin and the reflow process, thus it may effectively solve the bubble problem generated from resin filling process and lower reliability issue of the mechanical and electrical characteristics of the soldering joint in many times reflow heating process, and simplify the process steps of the chip package.
If the pitch among the conductive bumps of the chip is tiny, for example smaller than 100 um, and the surface flatness of the solder resist layer of the carrier is uneven, the bubbles gap will exist in the junctions while laminating the non-conductive film onto the surface of the chip, and pressing the non-conductive film onto the carrier. The wetting effect generated in high temperature may attach the non-conductive film effectively and seamlessly, but the temperature increases rapidly and shortly to lead the limitation of the wetting effect. Beside, the rapid increasing temperature leads the bubbles in the junction to expand to permeate into the non-conductive film having low elastic coefficient under high temperature. Thus, the bubbles may exist in the junction between the carrier and the non-conductive film, in the junction between the non-conductive film and the chip, and inside the non-conductive film. The existence of the bubbles in the junction or inside the film may cause the great risk of failure reliability for the device having the fine pitch of the conductive bumps.
Besides, comparing the prior liquid resin filling method for flip chip process, prior two-step thermo-compression flip chip process with the non-conductive film has higher equipment costs. The thermo-compression flip chip boning time is also about 2 to 3 times to the liquid resin filling method. Thus, for the industry, reducing the required investment cost for flip chip process with the non-conductive film has been emphasized.